Thermographic phospors in the gas phase

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Combustion processes that are turbulent will remain the base technology of technical energy conversion. A detailed knowledge of chemical, physical and coupled processes is required increasingly for the technologies of combustion. In particular it is important to understand the fields of flow and temperature. Simultaneous measurements of temperature and speed allow it to correlate both parameters. This is needed for the quantification of scalar fluxes and those are of eminent importance for the closing of the conservation equation that is used for the simulation.New developments towards a robust and quantitative temperature measurement are based on thermographic phosphors (TGP). TGPs are doped inorganic, crystalline solids with spectral properties that depend on temperature. The spectral and temporal emission changes with temperature and this is used for sensory purposes. Dopants are transition metals or rare earth elements. The use of TGPs for temperature measurements of the walls has been very successful. Adding TGP powders (particle diameter approx. 2 µm) to a fluid (gas or liquid) allows it to determine the temperature and the flow using particle image velocimetry (PIV). This is done by cross-correlation calculations of two Mie scattering images recorded consecutively. This method is of high potential for combined measurements of temperature and speed. From earlier studies it is concluded that the combination of PIV and TGPs will be very useful for measurements of scalar fluxes in hot gas applications and combustion environments under the following requirements: The precision for single shot measurements has to be increased and the signal-to-noise ratio above 1000 K has to be enhanced. The method is not yet used in combustion processes because there is a conflict of goals between the optimization of thermal and fluid dynamics and an enhancement of the signal-to-noise ratio.To overcome these limitations we will approach the goal of this research project on two tracks: 1) The TGPs will be optimized concerning quantum efficiency and cross section; 2) Hollow particles will be synthesized and tested for the application described above. Since it is very important that the particles fulfil the specifications dictated by the application it is mandatory that those who apply the particles to the combustion process collaborate closely with the experts that synthesize the TGPs. Both applicants of this proposal have shown in the past that their collaboration is very successful.